You can absolutely use road shoes in a triathlon, but tri-specific shoes are designed to save you precious seconds during transitions. They feature a single wide strap instead of multiple dials or straps, plus heel loops and pull tabs that let you slip your foot in quickly while already clipped into the pedals—many triathletes pre-mount their shoes on the bike and slide in during the ride.
The trade-off is that the single-strap design means fewer micro-adjustments for a precision fit, which matters less in a sprint or Olympic-distance race but might bother you on longer rides. If you're doing your first triathlon or only race occasionally, your road shoes will work fine. But if you're chasing personal bests and want every advantage in transition, dedicated triathlon shoes are a smart investment.